Strömgren photometric system (uvby) (sometimes also referred as Strömgren - Crawford photometric system) is four-colour medium-band photometric system

Photometric system

In astronomy, a Photometric system is a set of well-defined passbands , with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided.The first known...

 (plus H-beta filters) for stellar classification. It was pioneered by the Danish astronomer Bengt Strömgren

Bengt Strömgren

Bengt Georg Daniel Strömgren was a Danish astronomer and astrophysicist.Bengt Strömgren was born in Gothenburg. His parents were Hedvig Strömgren and Svante Elis Strömgren, who was professor of astronomy at the University of Copenhagen and director of the University Observatory in Copenhagen...

 in 1956 and extended by his colleague the American astronomer David L. Crawford in 1958.

Mean wavelength and half-widths of response functions

	u	v	b	y	βnarrow	βwide
Peak wavelength (nm)	350	411	467	547	485.8	485
Half-width (nm)	30	19	18	23	2.9	12.9

Indices

b-y, m₁, c₁, β

m₁ = (v - b) - (b - y)

c₁ = (u - v) - (v - b)

β = β_narrow-β_wide

y magnitudes are well-correlated with Johnson-Morgan V magnitudes.

External links

1. The Asiago Database on Photometric Systems
2. The uvby photometric system
3. Stromgren photometric system tutorial